As an optical information reader, bar code readers which read optical information of bar codes, two-dimensional codes, and the like indicating information such as names and prices of products are used widely by a distribution industry and a retail industry.
The bar code readers are roughly classified into hand-held ones held by one hand when in use and stationary ones, and the hand-held ones further include a pen type, a touch type, and a light beam scanning type (laser type).
A bar code reader of the light beam scanning type shapes light emitted by a light source such as a laser diode (LD) into a beam, deflects the light beam by a mirror so that the light beam hits on a bar code, and while rotating or vibrating (swinging) the mirror, scans the bar code so that the light beam moves across the bar code.
Then, reflected light from the bar code is condensed, and the condensed light is received by a light-receiving sensor such as a photodiode (PD), and is converted to an electrical signal. The electrical signal is coded after amplified and the resultant is output as bar code read information.
Such an optical information reader of the light beam scanning type is constituted as illustrated in FIG. 7 in a conventional example disclosed in, for example, PLT1.
The optical information reader illustrated in FIG. 7 includes a scanning/detecting part 50 having a laser diode LD and a photodiode PD, a scan mirror 60, and a signal processing part 70.
An oscillator 51 and a pulsed laser driver 52 in the scanning/detecting part 50 cause the laser diode LD to emit light with a predetermined frequency, and this laser light is passed through a collimator lens and an aperture, which are not illustrated, to be radiated as a laser beam. This laser beam is reflected by the scan mirror 60 which is vibrated back and forth by a drive circuit and a drive mechanism, which are not illustrated, and is made to scan a bar code 80 printed on a product or the like.
Reflected light from the bar code 80 is reflected again by the scan mirror 60, is condensed by a not-illustrated collector mirror or condenser lens, and is received by the photodiode PD of the scanning/detecting part 50. A current according to an amount of the received reflected light (light intensity) from striped light parts and dark parts of the bar code 80 flows in the photodiode PD, and its current output is converted to a voltage signal by a preamplifier 53.
This voltage signal is passed through a high pass filter (HPF) 54, and only a band component with a predetermined frequency or more is amplified by an AGC circuit 55, with a gain being automatically adjusted, and is detected by a synchronous detector 56 in synchronization with an oscillation cycle of the oscillator 51.
Its detection output signal is sent to the signal processing part 70 and is passed through a high pass filter (HPF) or a differential circuit 71, and only a high-frequency component is amplified again by an AGC circuit 72, with a gain being automatically adjusted, and becomes an analog output. The analog output of the AGC circuit 72 is passed through a low pass filter (LPF) 73, and the resultant becomes its control signal.
Further, the analog output is compared by a comparator 74 with a signal which is the same analog output having been smoothed by passing through a low pass filter (LPF) 75, and the result is binarized and is output as a binarized signal. Further, the same analog output is binarized by an edge digitizer 76 to be output as a binarized signal. These output signals are sent to a microcomputer (CPU), where the bar code is decoded (read).